The present invention relates to a system and method for rapid weighing of items. More particularly it relates to scales or weighing systems used in postage metering systems used to weigh and determine postage for mail pieces or the like.
Postal scale systems are well known. Such scale systems weigh a mail piece and determine the appropriate postage for that mail piece as a function of the weight. Postal mailing systems where a mail piece is transported onto a postage scale system, the appropriate postage is determined, and the mail piece is then transported to postage metering system for imprinting with a postal indicium representative of the postage determined are also known. One such system is described in U.S. Pat. No. 4,742,878; issued May 10, 1988. In such systems there is a constant need to increase the rate at which the scale can determine the weight of a mail piece in order that the throughput of the system can be increased.
U.S. Pat. No. 4,787,048; issued: Nov. 22, 1988, discloses one approach to decreasing the time required for a postage scale system to determine the weight of a mail piece. The system disclosed in this patent takes advantage of the structure of postage rate charts, i.e., the function that relates the weight of the mail piece to the appropriate postage amount. Such rate charge provides a constant postage value for all weights between a pair of predetermined weight breaks. The system of the ""048 patent takes advantage of this by use of an algorithm where a first estimate of the weight is made and used to determine the postage amount unless the first estimate is within a predetermined distance of a break point, in which case a second more accurate estimate is made.
While such systems have proven to be highly satisfactory for their intended purpose a basic problem remains that the weight of each mail piece in batches of mixed weight mail must be determined and the corresponding postage amount calculated before the vault (i.e. secure accounting registers which track postage expended by the meter to assure that the postal service receives payment for all mail pieces metered) can be debited for the postage amount and an appropriate indicium generated. As successive mail pieces are transported onto the scale system momentum from unbalanced rollers, mail piece collisions, spring reactions and the like is transmitted to the weight-sensing platform. These random excitations cause excessive displacements in the system transducer immediately prior to weight determination and increase the time required for the corresponding disturbances in the transducer output to decay sufficiently for an accurate weight to be determined.
Thus it is an object of the present invention to provide a method and system for decreasing the time required to determine the weight of items such as mail pieces.
The above object is achieved and the disadvantages of the prior art are overcome in accordance with the present invention by means of a scale system and method of operation of such scale system where the scale system includes: a transducer assembly; the transducer assembly in turn including, a transducer having a first member for supporting the item above a reference level, the first member producing a deflection proportional to the weight of the item, a clamping mechanism for clamping the first member to restrict deflection when activated, and a sensor for sensing the deflection and generating a signal representative of the weight as an output signal proportional to the deflection. The scale system further includes a platform for supporting the item during weighing, the platform being fixed to the first member, and a controller for controlling activation of the clamping mechanism.
In accordance with one aspect of the present invention the transducer is a load cell comprising; the first member, a second vertical member attached to the reference surface, and a pair of flexible members connecting the first and second members to form a four-bar linkage, so that the first member can be deflected relative to the reference surface in response to the weight of the item, and the sensor includes a strain gauge fixed to one of the flexible members.
In accordance with another aspect of the present invention, when activated the clamping mechanism applies a force to the first member transversely to the deflection.
In accordance with another aspect of the present invention the transducer and platform provide a vertically deflectable mechanism for supporting the item above a reference level, and operation of the scale system includes; clamping the mechanism as the item is transported onto the mechanism, releasing the mechanism after the item is positioned on the mechanism, and then analyzing the output signal to determine a weight for the item.
Other objects and advantages of the present invention will be apparent to those skilled in the art from consideration of the detailed description set forth below and the attached drawings.